The invention relates to a radiation-curable compound and a composition comprising this compound.
During radiation curing processes the transformation of the fluid applied film to a solid crosslinked network can be considered to progress through three distinct stages being induction, polymerisation and attainment of maximum cure plateau. (Chemistry and Technology of UV and EB formulations, Volume IV, Oldring, 1991, pages 8-12).
Factors which improve or inhibit cure rate are, for example, the lamp system (UV-dose, intensity, wavelength, IR-content) and the chemical system (reactivity, absorption, coating weight, pigmentation, temperature, oxygen inhibition and substrate).
For commercial coating operations, it is necessary that the coating achieves a tackfree surface within seconds or less, because the interval between application of the coating and stacking or rewinding of the coated substrate is very short. Failure of the coating to achieve a non-tacky surface in this brief interval will result in the layers of coated substrate (in a stack or roll) sticking together (xe2x80x9cblocking).
It is the object of the present invention to provide a coating composition having a high cure rate or rate of polymerisation and having the desired chemical and mechanical properies.
The radiation curable compound according to the invention is a mono or multi valent carboxylic ester of a compound containing a hydroxyalkylamidegroup and a hydroxygroup in which the carboxylic ester is derived from an xcex1,xcex2-ethylenically unsaturated carboxylic acid.
A radiation curable composition comprising the compound according to the invention results in high maximum polymerization rates.
According to a preferred embodiment of the invention the compound is a compound according to formula (I): 
where:
Y=hydrogen, an (C1-C8) alkyl group or 
R1, R2, R3, R4, R5, R6, R7, R8 are, identical or different, hydrogen or a lineair, branched or cyclic (C1-C8) alkyl chain,
R9=hydrogen, (C1-C5)alkyl, xe2x80x94CH2OH or CH2COOX,
R10, R11=hydrogen, (C1-C8) alkyl, (C6-C10)aryl or COOX,
X=hydrogen or (C1-C8) alkyl,
m=1-10,
p=1-4 and
n=1-10
R1, R2 or R3 may form part of a cycloalkyl group.
Preferably n=1-4.
Because of the resulting excellent reactivity characteristics m is preferably 1-4.
Preferably, p is 1 or 2
Preferably, Y is hydrogen.
Preferably, R1, R2, R3, R4, R5, R6, R7 and R8 are hydrogen or methyl.
R9 is preferably hydrogen or (m)ethyl.
R10 and R11 are preferably hydrogen.
The compound can be obtained, for instance, by an esterification reaction between a hydroxy functional hydroxyalkylamide and an unsaturated carboxylic acid, at a temperature between, for example, 80xc2x0 C. and 140xc2x0 C.
Preferably, 1-1.5 mol of acid are used per mole of hydroxide.
Preferably, the reaction takes place in the presence of an organic solvent, such as, for example, xylene, toluene or tetrahydrofuran.
Preferably, the reaction takes place in the presence of a stabilizing compound which prevents polymerization of the unsaturated ester groups under the conditions used for effecting this reaction. The stabilising compound or a mixture of stabilising compounds is generally used in amounts between about 50 and about 2000 ppm and preferably between 75 and 1000 ppm. They can be used in aerobic or anaerobic conditions depending on the stabilising compound.
Suitable stabilizing compounds include, for example, hydroquinone, monomethylhydroquinone, anthraquinone, xcex2-nitrostyrene, phenothiazine and 2,6-di-tert-butyl-4-methyl-phenol (BHT).
The esterification reaction may take place in the presence of a catalyst. Suitable catalysts include strong acids, for example, sulphur-containing organic acids like alkane sulphonic acids and methane sulphonic acid.
Suitable unsaturated carboxylic acids include, for example, (meth)acrylic acid and derivatives, crotonic acid, (semi-ester of) itaconic acid, maleic acid, citraconic acid, mesaconic acid and fumaric acid.
Preferably (meth)acrylic acid is applied.
The compound applied in the invention can also be obtained by the reaction between a hydroxy functional hydroxyalkylamide and an unsaturated carboxylic acid chloride, anhydride or ester.
Preferably, the reaction between the amide and the unsaturated chloride or anhydride takes place at temperatures between 0xc2x0 C. and 30xc2x0 C. in a solvent in the presence of a base. Suitable solvents include, for example, tetrahydrofuran, dichloromethane and diethylether. Suitable bases include, for example, pyridine and triethylamine.
Suitable chlorides, anhydrides or esters include the chlorides, anhydrides and esters of the in the foregoing mentioned carboxylic acids.
Preferably, the reaction between the amide and the unsaturated ester takes place at temperatures between 80xc2x0 C. and 140xc2x0 C. in the presence of a Lewis acid. Preferably, an excess of the unsaturated ester is applied. The ester functions both as solvent and as reactant. Suitable Lewis acids are, for example, tetra alkyl titanate and sulphuric acid.
According to a preferred embodiment of the invention the preparation of the compound according to the invention takes place by reaction between a hydroxy functional oxazoline and an unsaturated carboxylic acid.
Such a reaction can, for example, take place at a temperature between 50xc2x0 C. and 140xc2x0 C.
Suitable hydroxy functional oxazolines include, for instance, hydroxy functional (C1-C20) alkyloxazolines, for instance, xcex2-hydroxy ethyl oxazoline and xcexa9-hydroxy undecyloxazoline.
Suitable unsaturated carboxylic acids include, for example, (meth)acrylic acid and derivatives, crotonic acid, (semi-ester of) itaconic acid, maleic acid, citraconic acid, mesaconic acid and fumaric acid. Preferably, (meth)acrylic acid is used.
Preferably the hydroxy functional oxazolines are prepared from, for instance, a lactone and an ethanolamine or 2-propanolamine. Suitable lactones are for instance propiolactone, butyrolactone, valerolactone and caprolactone.
An advantage of the hydroxy functional compound according to the invention is that the hydroxy group gives the possibility for attaching this compounds to a polymer. A suitable method to obtain the attachment is to react first the hydroxyl functional compound with a diisocyanate and to react subsequent with an hydroxy functional polymer. Suitable diisocyanates are, for example, toluene diisocyanate, hexane diisocyanate, isophorone diisocyanate or 3,4-isocyanate methyl-1-methyl cyclohexyl isocyanate (IMCI). Suitable hydroxy functional polymers are, for example, hydroxy functional polyethylene, polypropylene, polyester, poly(meth)acrylate, polyamide, polyether, polyisobutylene, polyacrylonitrile, polyurethane and polylactone.
Additives can also be connected via the hydroxy functionality of the hydroxy functional compound according to the present invention.
Suitable additives include for example, adhesion promoters, disperging agents, photo initiators and synergists.
The compound according to the invention can be cured by means of a free-radical reaction. In these reactions the free radicals can be obtained by radiation initiation.
Radiation-curing preferably takes place by means of, for example, a photochemical process such as, for example, ultraviolet radiation (UV) or a radiation-chemical process such as electron beam (EB).
UV and EB radiation are explained in greater detail by for example Bett et al. in the article entitled xe2x80x9cUV and EB curingxe2x80x9d (Jocca 1990 (11), pages 446-453).
The amount of the compound according to the invention can range between 0,01% by weight and 100% by weight in a composition according to the invention.
Generally, the radiation curable composition according to the invention is substantially solvent free.
The composition according to the invention can be used, for example, in coating compositions, inks and adhesives.
If desired and depending on the application, the compound can be combined with oligomers or polymers which are based, for example, on (meth)acrylate units, maleate units, fumarate units, itaconate units, vinylester units, vinylamide units and/or vinylether units.
Due to the relatively high cure speeds the present compounds can also be applied as additives for enhancing the cure speed of a formulation. In general such additives are used in amounts ranging between 0,01% and 25% by weight and preferably in amounts between 0,5% and 10% by weight relatively to the total amount of all ingredients.
After curing, the coatings according to the invention have many desired properties such as for example good chemical properties (resistance to solvents, acids, alkali and moisture), good optical properties and appearance, good mechanical properties (such as hardness, flexibility, adhesion, abrasion resistance, strength and durability), good thermal stability and good weatherability.
The composition comprising the radiation curable binder composition may further comprise pigments, stabilisers and other additives.
The radiation curable formulation generally consists of a prepolymer, a reactive diluent and additives. Two other possible components, depending upon the type of formulation and cure mechanism are pigments and photoinitiator system.
The compound according to the invention can for example be applied in a water based coating composition, in a solvent based coating composition, in a high solids coating composition, in a 100% solids coating composition and in a powder paint composition.
The most preferred irradiation source is ultraviolet light. Ultraviolet light is preferably high intensity light to provide a dosage to achieve reasonable curing rates. In the event that lower energy light is to be applied, it may then be desired to subject the compositions also to elevated temperatures in order to reduce the time for adequate polymerization to occur.
With respect to UV curing equipment we refer to, for example, pages 161-234 of Chemistry and Technology of UV and EB-formulations, Volume 1, Oldring, 1991.
Suitable lamps employed to provide the desired high intensity and availability of wavelength and spectral distribution include for example that available from Fusion Systems, Corp.
A composition according to the present invention can be applied on substrates such as, for example, plastic, paper, board, leather, glass, wood and metal.
This composition is preferably polymerised in the presence of a photoinitiator but it is also possible to polymerise in the absence of a photoinitiator.
Suitable photoinitiators allow for initiation of the curing process with exposure to light having wavelengths between about 200 nm and about 600 nm. Suitable photoinitiators have ketone functionalities and can be aromatic such as, for example, benzophenone. Darocur 1173(copyright) (Ciba) is a suitable benzyl-ketal-based photoinitiator, which contains 2-hydroxy-2-methyl-1-phenylpropane-1-one as an active component. Irgacure 184(copyright) (Ciba) is an aryl ketone containing hydroxycyclohexyl phenyl ketone as active component, and is a suitable photoinitiator. Irgacure 369(copyright) (active component 2-benzyl-2-dimethylaminol-1-(4-morpholinophenyl)-butanone-1) is also suitable. Acyl phosphines, such as for example 2,4,6,-trimethylbenzoyl diphenyl phosphone oxide (Lucerine TPO(copyright), BASF) can also be used, as can Quantacure CPTX(copyright) (Octel Chemicals), which contains 1-chloro-4-propoxy thioxanthone as active component. Chemical derivatives of these photoinitiators are suitable, as are mixtures of these photoinitiators. A suitable combination of photoinitiators is Irgacure 1800(trademark) (Ciba) consisting of 75% by weight Irgacure 184(trademark) and 25% by weight (bis-(2,6-dimethoxy benzoyl)-2,4,4-trimethylpentyl fosfine oxide). Other suitable photoinitiators can be of the Norrish-II-type, for example, the combinations benzophenone with amine, maleimide with amine, thioxanthone with amine and antrachinon with amine.
The invention is explained by reference to the following non-restrictive examples.
In the following the cure behaviour is monitored with xe2x80x9creal time infra red spectroscopyxe2x80x9d. The conversion of the double bonds during the photopolymerisation was monitored by means of infrared (Bruker IFS55).